The present invention relates generally to hydroplane boats, and more particularly to hydroplane boats having a "deep-V" or a "stepped hull" design.
Hydroplane boats are boats capable of skimming over water with the hull raised wholly or partly clear of the water surface. Boats with this capability have many different designs, but two such designs are of particular pertinence to the present invention. These are the "deep-V" design, generally accepted as the best design for performance in rough water, and the "stepped hull" design, offering the lowest drag and highest speeds among single hulled boats.
In the "deep-V" design, the hull has a continuous surface from bow to stern with a ridge down the central portion thereof, forming a "V" shape when viewed from the stern. The deadrise of such a boat, that is, the angle between the hull surface and a horizontal plane, is generally twenty degrees or more. "Deep-V" boats have an undesirable tendency to pitch severely in rough seas in resonance with the frequency of the wave action. Further, they require powerful, heavy, and uneconomic engines to achieve planing and to overcome the friction between the hull and the water. The lifting characteristics of the continuous hull result in a non-level ride, and the boat exhibits lateral instability at rest. In high speed turns such a boat banks severely, and a large turning radius is required for low speed turns because the boat pivots on its bow. Trim tabs or similar devices are often necessary to provide the necessary lift at the stern area, depending on the orientation of the power unit.
In the "stepped hull" design, the hull comprises two generally flat sections separated by a discrete step running transverse of the hull. When the boat is in motion a vacuum is created just aft of the step as the water pulls away from the hull. To alleviate the vacuum, air is supplied to this area by external vents located in the chine area of the hull. Such external vents, however, create structural weakness in this region of the boat and degradation of the directional stability associated with boats having continuous chines. Also, loss of air supply to the area aft of the step will occur if the vents are even momentarily blocked for any reason, as for example if engulfed by a large wave. The vacuum resulting from such a loss of air supply can lead to an abrupt cessation of planing, causing the boat to slow suddenly in the water. Other disadvantages of a stepped hull design result from the generally flat nature of the hull surfaces. The considerable lifting force exerted on the stern by the flat hull surface causes the bow to plow under the high waves and, in a following sea, may cause the boat to broach by pivoting on the step. Also, without a keelson in the aft portion of the hull surface, a certain amount of directional instability arises.
Although hydroplane boats have been built which attempted to combine the "deep-V" and "stepped hull" designs, such boats have not included continuous chines from stem to stern for structural strength and directional stability, nor have they overcome the problem of sudden deplaning from loss of air supply to the area aft of the step.